Machine and process for making a sheet of single face corrugated cardboard

ABSTRACT

A machine for manufacturing a sheet of corrugated board by gluing a fluted sheet of board onto a liner sheet of board includes: a fluted cylinder, a central fluted cylinder equipped with an assembly for applying the fluted sheet against its periphery, a smooth cylinder for bringing the liner sheet into contact with the crests of the flutes of the fluted sheet, and a motorized smooth heating cylinder situated downstream of a path of the corrugated board and entirely at distance from the first three cylinders; an assembly for controlling and adjusting the rotational speed of the motorized smooth heating cylinder; and an assembly for adjusting and maintaining during operation the pressure of the liner sheet on the flutes of the fluted sheet over a line of contact below 3 kg/cm. The fourth cylinder presses the fluted sheet onto the central fluted cylinder over an circular arc corresponding to a subtended angle between an order of 30° and an order of 80°. The fourth cylinder contacts with the back of the liner sheet over an circular arc corresponding to a subtended angle between an order of 90° and an order of 200°.

FIELD OF THE INVENTION

The present invention relates to the manufacture of corrugated board andmore particularly to a machine for manufacturing a sheet of single facecorrugated board by glueing a fluted sheet of board onto a flat sheet ofboard, termed liner sheet, of the type comprising three heatingcylinders which are substantially tangential in pairs, with parallelaxes, namely a first fluted cylinder for preforming the fluted sheet, asecond, central, fluted cylinder associated with means for applying thefluted sheet against its periphery, and a third, smooth, cylinder forbringing the flat sheet into contact with the flutes of the fluted sheetat the periphery of the second cylinder, as well as means for coatingthe said flutes with glue before the contact between fluted sheet andliner sheet.

It also relates to a process for manufacturing sheets of single facecorrugated board, particularly using a machine of the above type.

It finds a particularly important, although not exclusive, applicationin the field of the manufacture of single face sheets at high speedusing board obtained from low grammage (less than of the order of 150g/m²) recycled paper.

DESCRIPTION OF THE PRIOR ART

Machines of the above-defined type are already known.

FIG. 1 thus represents a machine 1 of the prior art in a line 2 formanufacturing single face corrugated board.

The line comprises means 3 and 4 respectively for feeding flat, linersheet and flat sheet which is intended to form the fluted sheet.

These feed means comprise, in a way which is itself known, reel unwindstands 5 which allow good control of the unwinding and of the brakingwhich are necessary for the manufacture of the board.

They also comprise a preheater 6 for the liner sheet, generallyconsisting of a steel cylinder heated by steam and equipped with smallrolls termed "turn rolls" which serve to vary the paper/cylinder contactarea, and a preconditioner 7 for the fluted sheet, which for its partand furthermore includes a boom for moistening the sheet, which promotesthe formation of the flutes.

The line 2 moreover comprises means 8 for discharging the single faceboard obtained, these means consisting of a system of belts at the toppart of the line.

FIG. 2 shows more precisely, in a sectional view, the single facemachine 1 of the line of FIG. 1.

It comprises, on the fluted sheet feed side, an additional preheatingcylinder 9 and a moistening cylinder 10 and, on the liner sheet feedside, two rotating preheating cylinders 11.

The machine 1 moreover comprises a first, top, fluted cylinder 12 madeof stainless steel. It is hollow and designed to be heated with steam ina way which is itself known.

The machine 1 also comprises a second, central, fluted cylinder 13 madeof stainless steel of axis parallel to that of the first cylindersubstantially tangential to the latter and, for example, of the samediameter.

The second cylinder is, for example, of the type known under the name"Air Drive", manufactured by the French company MARTIN.

It includes two chambers, namely a central steam-heated chamber and avacuum chamber 15 connected to a device 16 for forming a vacuum. Thechamber comprises ducts 17 pierced along the entire length of thecylinder and communicates with the fluted peripheral surface via holes.

The machine 1 comprises a third, bottom, cylinder 18 with a smoothsurface, of axis parallel to the first two and, for example, of the samediameter. This cylinder is heated with steam in a similar way to thefirst two and is designed to compress the liner sheet against the crestsof the flutes of the fluted sheet, in contact with the periphery of thecentral fluted cylinder, as will be seen.

The machine 1 moreover comprises means 19 for coating the crests of theflutes with glue, these means being in themselves known, and comprisinga laminating roll 20, a bath of glue 21 and a glueing roll 22.

The operating principle of the machine 1 is as follows.

Two sheets or webs of paper in board 23 and 24 are introduced into themachine 1.

The sheet 23 is intended to form the fluted sheet.

After a drying and moistening treatment at 7, 9 and 10 it passes aroundthe first fluted heating cylinder 12, over a part of its periphery.

It is then introduced between the two fluted heating cylinders 12 and 13which rotate in opposite directions from one another, like two gearingcylinders.

The vacuum created in the lower part of the cylinder 13 then presses thefluted sheet 23 formed against the heating cylinder of a circular archaving a vertex angle equal to of the order of 180°.

When it passes over the face of the glueing roller 22, a line of glueis, moreover, and as has been seen, deposited at the crest of theflutes.

The glue is, for example, based on starch.

The liner sheet 24 is, for its part, introduced at the bottom and on theopposite side of the machine 1.

It is predried at 11 and wound around the third cylinder 18, which isalso called a smooth press cylinder. A very strong hydraulic pressure,for example of 5 kg/cm (line pressure) ensures successive contact at 25(see FIG. 3) between each top crest of the flutes of the fluted sheet 23and the liner sheet 24 made of smooth paper.

The glue joint is thus obtained through the combined action of the highpressure and of the temperature in a fraction of a second.

Entrainment of the sheets is achieved by traction, the fluted sheetbeing entrained by the meshing of the fluted cylinders 12 and 13, andthe liner sheet being entrained by being trapped between the centralcylinder 13 and the smooth cylinder 18.

Other types of single face machines exist, such as those in which thefluted sheet is pressed onto the central cylinder by air, instead ofbeing sucked on by vacuum, for example.

Their operating principle and the structural elements which they employin general, however, remain identical to those described hereinabove.

Although they allow high throughput rates to be achieved, giving anacceptable single face paper, the known machines do, however, stillexhibit drawbacks.

In particular, in order to obtain good glueing, which is the desiredobjective if a good quality corrugated board is desired, it was hithertobelieved that it was necessary to press the two sheets one on the otherwith very high pressure, it being moreover understood that a sufficienttemperature is maintained at the moment of glueing to allow the glue togelatinize.

Unfortunately, and in particular, this pressure gives rise totroublesome effects.

It is in fact applied to the top part of the crests of the flutes (seeFIG. 3) which causes the board to be cut, especially at resonant speeds,or alternately at high speeds.

Furthermore, since the pressing cylinder 18 is applied against thecentral fluted cylinder 13 discontinuously, from one flute to another,vibrations and significant noise (105 to 110 decibels at high speed) aregenerated.

This results in a poor quality corrugated board, in which thecharacteristics of moisture-resistance and burst strength of the linersheet, for example, are lessened.

SUMMARY OF THE INVENTION

The present invention aims to provide a machine and a process formanufacturing single face corrugated board which meets the practicalrequirements better than those known before, especially in that it makesit possible to practically eliminate cuts of paper at resonant speedsand/or at high speed, that is to say for example speeds of above 300m/min, and in that it makes it possible to obtain excellent glueing,which produces a corrugated board of improved performance and does sofor low cost and in a way which is easy to implement.

The existing machines may, moreover, easily be adapted to profit fromthe improvement that the present invention constitutes.

In order to do this, the present invention starts off from an entirelynew idea consisting especially in considerably reducing the pressure, oreven eliminating it completely, between the fluted cylinder 12 and thesmooth cylinder 18 on the surface for contact between the sheets, anddoes so in complete contrast to the teachings of the prior art,replacing the high pressure by prolonged heating of the sheets againsteach other.

To this end, the present invention particularly proposes a machine formanufacturing a sheet of single face corrugated board by glueing afluted sheet of board onto a flat sheet of board, comprising threeheating cylinders which are substantially tangential in pairs, withparallel axes, namely a first fluted cylinder for preforming the flutedsheet, a second, central, fluted cylinder associated with means forapplying the fluted sheet against its periphery, and a third, smooth,cylinder for bringing the flat sheet into contact with the flutes of thefluted sheet at the periphery of the said second cylinder, and means forcoating the said flutes with glue before the said contact, characterizedin that it additionally includes a fourth, smooth, rotary, heatingcylinder of axis parallel to the other cylinders, situated downstream ofthe path of the corrugated board with respect to the said othercylinders and designed to press the fluted sheet onto the secondcylinder over a circular arc corresponding to a subtended angle of afirst given value, and to be itself in contact with the back of the flatsheet over a circular arc corresponding to a subtended angle of a secondgiven value.

Advantageously, means for controlling and adjusting the rotational speedof the said fourth cylinder with respect to the rotational speed of thesaid second cylinder (or, which is the equivalent, to the speed oftravel of the corrugated board) are moreover provided.

In advantageous embodiments, recourse is additionally had to one and/orother of the following provisions:

the first given value is between of the order of 30° and of the order of80°;

the first value is of the order of 60°;

the second given value is between of the order of 90° and of the orderof 200°;

the second given value is of the order of 180°;

the fourth heating cylinder has the same diameter as the first threeheating cylinders;

the machine additionally includes a small smooth cylinder of axisparallel to the axis of the said heating cylinders, situated downstreamof the said cylinders in the path of the corrugated board and beneaththe horizontal plane tangential to the upper generatrix of the fourthcylinder;

the machine includes means for adjusting pressure of the liner sheet onthe flutes of the corrugated sheet, below a given threshold value Po,for example of the order of 3 kg/cm (0≦Po<3 kg/cm);

the machine includes means for maintaining the distance between thesurfaces of the second and third cylinders which are designed toeliminate any pressure of the third cylinder on the fluted and linersheets of the corrugated sheet in contact with the second cylinder.

Such a system in fact gives excellent results even at speeds ofprogression of the board of 200 m/min.

The invention also proposes a manufacturing process using a machine asdescribed hereinabove, and more particularly a process for manufacturinga sheet of single face corrugated board, starting from a sheet of flutedboard and from a flat sheet of board, termed liner sheet, by glueing oneonto the other, characterized in that the crests of the flutes of thecorrugated sheet which have been coated with glue beforehand are kept incontact with the flat sheet over a first zone formed by a first surfaceportion of a heating central fluted cylinder designed to press the saidfluted sheet against the said first surface portion, over an arccorresponding to a subtended angle of a first given value, and over asecond zone formed by a second surface portion of a rotary heatingsmooth cylinder situated downstream of the path of the corrugated boardwith respect to the central cylinder, designed to press the said linersheet against the said second surface portion over an arc correspondingto a subtended angle of a second given value.

In advantageous embodiments, recourse is additionally had to one and/orother of the following provisions:

the first given value is between of the order of 30° and of the order of80°;

the first given value is of the order of 60°;

the second given value is between of the order of 90° and of the orderof 200°;

the second given value is of the order of 180°

the speed of the heating smooth cylinder is set to a speed of between ofthe order of 1.02 V and of the order of 1.25 V, advantageously 1.06 V, Vbeing the speed of travel of the corrugated board formed;

a pressure is applied between the flute crests and the liner sheet atthe first point of contact after glueing, the value of this pressurebeing less than 3 kg/cm;

no pressure is applied by the third cylinder to the fluted and linersheets of the corrugated sheet in contact with the second cylinder (zeroline pressure).

The invention will be better understood from reading the description ofone embodiment of the invention which is given hereinafter by way ofnonlimiting example.

BRIEF DESCRIPTION OF THE DRAWINGS

The description refers to the accompanying drawings in which, inaddition to FIGS. 1 to 3 which have already been described relating to amachine of the prior art:

FIG. 4 diagrammatically shows one embodiment of the improvement that theinvention constitutes, in transverse section.

FIG. 5 is a diagrammatic section on V--V of the fourth cylinder of FIG.4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The machine according to the embodiment of the invention moreparticularly described here on the one hand comprises a single facemachine of the type described with reference to FIG. 2 and, on the otherhand, comprises a fourth cylinder set out as will be describedhereinbelow with reference to FIG. 4.

In order to simplify, the same reference numerals are used when theydenote the same elements.

In addition to the first, second and third cylinders 12, 13 and 18described with reference to FIG. 2, the machine according to theinvention includes a fourth, heating, smooth cylinder 26 of axis 27parallel to the axes of the previous cylinders and situated above these,for example directly after the second cylinder in the path of the sheetof corrugated board.

This cylinder is heated with steam in a similar way, for example toreach an outer surface temperature of the cylinder of between 160° C.and 200° C.

It is made of a stainless steel and, for example, has an identicaldiameter to the others.

Means (not represented) for adjusting the rotational speed of thecylinder 26, which means are known in themselves, are provided. Theratio of speeds of the cylinder 26 and of the travel of the board can

12 therefore be adjusted to provide tension in the liner sheet which iswound over and in contact with the smooth surface of the cylinder.

With a machine thus modified, glueing is different from conventionalglueing. Instead of making the glued joint instantaneously through thecombined action of the heat and of a high pressure, glueing is ensuredessentially by the heat, the pressure being substantially reduced.

The glue is dried in two zones:

a first zone 28 of contact between the fluted sheet 23 and liner sheet24, where the two sheets are held one against the other on the centralfluted cylinder 13 over a wound angle α, for example of approximately60°.

At the point 29 where the two sheets are joined together, the spacebetween the central fluted cylinder 13 and the smooth third presscylinder 18 is moreover maintained at a fixed value by adjustable limitstops so that the pressure is zero or low, for example lying between 0and 3 kg/cm, and does not damage the sheets;

a second contact zone 30, where the two sheets are again held oneagainst the other but this time on the cylinder 26 over a winding angleβ, for example of 180°, which makes it possible to completegelatinization and drying of the glue.

Advantageously, if V is the speed of travel of the board, and V1 is theexternal speed of the cylinder 26, V1 [sic] is between of the order of1.02 V and of the order of 1.25 V.

In the embodiment more particularly described here, and in order to keepthe sheet of corrugated board on the fluted side in contact with thefluted surface of the cylinder 13 over an angle α, the cylinder 26, atleast with respect to the plane tangential to the point of contact 29with the cylinder 13, has a part of its surface on the same side as thesaid cylinder 13.

In order to do this, the axis 27 of the cylinder 26 may also be situatedon the same side (not represented on FIG. 4, which shows an alternativeon the opposite side) as the cylinder 13, with respect to the verticalplane passing through the axis 31 of the smooth cylinder 18.

In order to keep the sheet of corrugated board, on the smooth side, incontact with the cylinder 26 over an angle β, a small smooth and solidroll 32, known in itself, and able to be in contact with the sheet ofcorrugated board, on the corrugated side, is, for example, provided.

In order to do this, it has, for example, a lower generatrix 33 situatedbeneath the horizontal plane 34 tangential to the upper generatrix ofthe cylinder 26.

Advantageously the axis 35 of the cylinder 32 is situated beneath theaxis 27 of the cylinder 26.

Sufficient distances e and e' between side walls, respectively of thecylinders 13 and 26 and 26 and 32, are moreover provided in order toallow the sheet of board 36 formed to progress correctly.

FIG. 5 shows a diagrammatic section on V--V of the cylinder 26.

It comprises two cylindrical ends 37 and 38 mounted on bearings 39 and acylindrical body 40, for example made of stainless steel or cast iron,equipped with a central recess 41 fed with steam at 42 via the end 37.

The steam circulates inside the recess and is discharged at 43 via thesame end 37. A variable-speed motor 44 makes it possible to vary therotational speed of the cylinder 26 in a way which is known in itself,as a function of the desired tension for the corrugated board.

The smooth surface of the cylinder 26 allows possible sliding, allowingslippage which takes up any possible play.

By virtue of the invention, a significant improvement in characteristicsof the single face corrugated board produced has been observed.

In particular, and for example, with all other things moreover beingequal, an improvement at least of the order of 20% in the Cobb moistureresistance was observed, and a 10% improvement in the burst strength ofthe liner was observed, by comparison with a machine of the type of thatof FIG. 2.

More generally, a device according to the invention preserves the Cobbmoisture resistance qualities of the liner paper, without detrimentalchange, contrary to that which is observed with the devices of the priorart.

We claim:
 1. Machine for manufacturing a sheet of single face corrugatedboard by gluing a fluted sheet of board onto a liner sheet of board,with a preset speed of travel of said corrugated board, the machinecomprising;three heating cylinders which are substantially tangential inpairs, with parallel axis, being a first fluted cylinder for performingflutes of the fluted sheet in which said flutes having crests, a second,central, fluted cylinder equipped with means for applying the flutedsheet against the periphery of the second cylinder, and a third, smooth,cylinder for bringing the liner sheet into contact with the crests ofsaid flutes of the fluted sheet, under a pressure and over a line ofcontact parallel to said axis situated at the periphery of said secondcylinder; means for coating the crests of said flutes with glue beforesaid line of contact; a fourth, motorized, smooth, heating cylinder aaxis parallel to said three heating cylinders, situated downstream of apath of the corrugated board with respect to said three heatingcylinders, entirely at distance from said three cylinders, said fourthcylinder having an adjustable rotational speed and being designed topress the fluted sheet onto the second cylinder over a first circulararc corresponding to a first subtended angle of a first given valuecomprised between of an order of 30° and of an order of 80°, and saidfourth cylinder being in contact with a back of the liner sheet over asecond circular arc corresponding to a second subtended angle of asecond given value comprised between of an order of 90° and of an orderof 200°; means for controlling and adjusting said rotational speed ofsaid fourth cylinder with respect to the preset speed of travel of thecorrugated board; and means for adjusting and maintaining duringoperation, the pressure of the liner sheet on the flutes of the flutedsheet over said line of contact by the third cylinder, below a giventhreshold value of 3 kg/cm.
 2. Machine according to claim 1, wherein thefirst given value is of an order of 60°.
 3. Machine according to claim1, wherein the second given value is of an order of 180°.
 4. Machineaccording to claim 1, wherein the fourth heating cylinder has a samediameter as the first three heating cylinders.
 5. Machine according toclaim 1, further comprising a fifth, smooth cylinder having axisparallel to the axis of the first four cylinders, situated downstream ofthe first four cylinders in the path of the corrugated board and beneatha horizontal plane tangential to an upper generatrix of the fourthcylinder.
 6. Machine according to claim 1, further comprising means formaintaining the distance between surfaces of the second and thirdcylinders, which are designed to eliminate any pressure of the thirdcylinder on the fluted and flat sheets of the corrugated sheet incontact with the second cylinder.
 7. Process for manufacturing a sheetof single face corrugated board with a preset speed of travel of saidcorrugated board, comprising the steps of:feeding a sheet of boardmaterial between first and second heating corrugated cylinders to form afluted board around said second heating corrugated cylinder, said secondheating corrugated cylinder having an axis, said fluted board havingparallel flutes presenting parallel crests to said axis of the secondcylinder; coating the crests of said flutes with glue; bringing intocontact a liner sheet, which is supplied by a third heating cylinder,with said crests over a line of contact parallel to said axis of thesecond cylinder; applying and maintaining during operation a pressure onsaid crests by said third heating cylinder, over said line of contact,of a value less than 3 kg/cm; keeping the fluted board, after said lineof contact, in contact with the liner sheet over a first zone formed bya first surface portion of said second cylinder, over a first arccorresponding to a first subtended angle of a first given valuecomprised between of an order of 30° and of an order of 80°; and furtherkeeping said timed board in contact with said liner sheet over a secondzone formed by a second surface portion of a rotary heating smoothfourth cylinder situated distantly apart from the second cylinder anddownstream of a path of the fluted board with respect to the secondcylinder, said fourth cylinder having a rotational speed and beingarranged to have said liner sheet pressed against the surface portionover a second arc corresponding to a second subtended angle of a secondgiven value comprised between of an order of 90° and of an order of200°.
 8. Process according to claim 7, wherein the first given value isof an order of 60°.
 9. Process according to claim 7, wherein the secondgiven value is of an order of 180°.
 10. Process according to claim 7,wherein the rotational speed of the fourth cylinder is set to a speed ofbetween an order of 1.02 V and an order of 1.25 V, V being the presetspeed of travel of the corrugated board.
 11. Process according to claim7, wherein a speed of the third cylinder is of an order of 1.06 V, Vbeing the preset speed of travel of the corrugated board.
 12. Processaccording to claim 7, wherein the value of the pressure applied by thethird heating cylinder on said crests over said line of contact, duringoperation is 0 kg/cm.